The invention relates to a device for providing a flux layer on a printed board, which device comprises a reservoir and a wire-gauze cylinder which is rotatable in the reservoir, while in the cylinder a spray tube extending parallel to its center line is accommodated, into which spray tube the outflow aperture of an air supply line opens and in which spray tube spray apertures have been provided which are arranged in a row extending in the longitudinal direction of the spray tube.
For soldering parts to a printed board it is customary to wet such a panel with a flux with a view to the removal of contaminations and the furthering of the soldering activities. When a device is used as described in the opening paragraph the board is for that purpose moved transversely to the longitudinal direction of the spray tube over the wire-gauze cylinder which rotates during operation and the flux which is dragged along by the cylinder out of the liquid bath in the reservoir is blown against the printed board to be wetted by means of the air flowing out of the spray apertures in the spray tube.
In a known device, which is now commercially available, the spray tube has a small diameter as compared with the diameter of the cylinder and a second duct which extends parallel to the spray tube and is connected to a sources of compressed air is accommodated in the cylinder, which duct communicates with the interior of the spray tube by means of a number of radially extending connecting studs connected to the spray tube. The spray apertures provided in the spray tube for the exhaust of the compressed air have a cylindrical shape.
It has been found in practice that with this known device a regular spray pattern cannot be obtained so that a flux layer of a non-uniform thickness is formed on the board to be wetted, which impedes an efficacious cleaning of the printed board and an effective provision of reliable soldered joints. The non-uniform layer thickness is caused by air whirls and by a non-uniform pressure distribution of the air flowing out of the spray apertures over the length of the tube. The thicker the flux layer, the more residues remain on the wiring panel. Because residues cause contact problems, for example, in the in-circuit-testing of printed boards by means of pin beds, thin flux layers are desired. Because thin flux layers are necessary and desired, the spreading on the layer thickness is of great influence.